This invention relates to an improved method and means for pulling great lengths of fiber optic cable through a buried or underground conduit.
Fiber optic cable is comprised of a bundle of glass fibers or other transparent material enclosed within a protective outer sheath. The fiber optic cable is normally wound upon reels which are transported to the job site by reel haulers, trucks, etc. The fiber optic cable is normally pulled through the underground conduit by means of a rope connected at one end thereof to the lead end of the fiber optic cable. The rope is normally pulled through the conduit by some sort of pulling apparatus. The friction of the fiber optic cable being pulled through the conduit has heretofore limited the lengths of the cable which could be pulled due to the tension limits or strength of the cable. Such pulling limitations resulted in the necessity of splicing together shorter lengths of the fiber optic cable which is time consuming and expensive. In addition, the transmission quality of the cable is affected by a large number of splices.
An attempt was made to solve the problems associated with pulling long runs of fiber optic cable and the same is described in U.S. Pat. No. 4,576,362 issued to Ralph C. Langston on Mar. 18, 1986. In the Langston apparatus, a first cable puller is positioned at the conduit exit with a second pulling apparatus being provided at an intermediate access point along the length of the conduit through which the cable is being pulled. Both of the pulling machines of the Langston patent involve capstan winches. The Langston method utilizes a positive pull by the lead puller to tighten the cable on the booster capstan drive. The Langston method requires approximately sixteen percent of the booster pulling tension to snub the cable on the booster capstan. Therefore, a cable that requires 600 pounds pull to move must be snubbed with approximately 100 pounds pull to obtain proper friction on the booster capstan drive. On an optic fiber cable pull of considerable length, any additional drag at the inlet of the conduit will be amplified about five times at the outlet. Therefore, a drag of 100 pounds to snub the booster capstan may require 500 pounds extra pull by the lead puller. Therefore, on pulls of considerable length, the effective pull required by the lead puller that snubs the cable on the booster capstan may be cut to below one-fourth. A further disadvantage of the Langston method is that the fiber optic cable must be coiled on the booster puller which results in cable twisting when the cable is removed from the booster puller.